The present invention relates to a free radical polymerization, and more particularly to a free radical polymerization for preparing polymers with low polydispersity index.
Recently, with increased maturity of polymer technologies, polymer applications are involved in not only traditional plastic and synthetic resin industries but also high technology industries such as electronics, optoelectronics, communications and biotechnologies. Some relative polymer materials with specific properties are critical for related industries. For example, photoresistant reagents for preparation of nano-type devices and nano-polymer hybrid materials for dramatically enhancing mechanical properties are all much sought after.
The properties of polymer materials are dependent on configuration. For example, polymerization degrees, molecular weight distribution and components thereof behave in relation to the performance of the polymer materials. The traditional active cation and anion polymerization methods can be used to control the polymerization degree of some monomers and narrow distribution of molecular weight. However, they are limited in their ability to further narrow molecular weight distribution, resulting in polymer products with polydispersity index (defined as the ratio of the weight average molecular weight to number average molecular weight, Mw/Mn) generally more than 2. As well, the variety of monomers applied to the above polymerization methods is limited, and strict reaction conditions and long reaction times thereof also restrict use in related industries.
In 1998, CSIRO disclosed an active free radical polymerization method called reversible addition-fragmentation chain transfer process (RAFT process) to prepare polymer products with narrow molecular weight distribution and further control the polymer chain length. The so-called RAFT process is a combination of general procedures for traditional free radical polymerizations with the addition of a fixed amount of reversible addition-fragmentation chain transfer reagent (RAFT reagent).
However, it is very inefficient for conventional active radical polymerization with RAFT reagent, since monomers produce polymerization only under nitrogen atmosphere and very dilute solution conditions to provide polymer products with narrow molecular weight distribution. Therefore, the above problem causes longer reaction time and incomplete reaction of polymerization, making it neither economical nor convenient.
Mays et al. in WO 02/079269 disclose a free radical polymerization process with ionic liquid, substituting general organic solvent, as solvent. The polymerization can be performed completely within 4 hours, thereby increasing the efficiency of polymerization. Due to inferior compatibility between the employed ionic liquid and monomers, the polymers prepared by the process have wider molecular weight distribution. Thus, the described free radical polymerization process cannot meet current market demands for reducing PDI to less than 1.5. Therefore, a novel free radical polymerization process for further reduction of PDI of obtained polymer products is desirable.